Charged-particle triggered discharge for a laser

ABSTRACT

Method and apparatus for triggering a discharge in a laser utilizing charged particles. A source of charged particles injects a beam of charged particles throughout the discharge volume of a laser to create uniform ionization therein and thus trigger the electrical discharge needed to excite the lasing medium. This allows the applied electric field to be optimized for excitation without regard to the field required to initiate the discharge in an un-ionized fluid. The beam of charged particles initiates the discharge by providing an initial ion and electron population within the discharge volume. The charged particle beam may be created by several means including a radioactive source, or artificial sources such as electron guns, particle accelerators, or other devices which produce a directed flow of charged particles with sufficient energy to penetrate the active lasing fluid over the entire discharge volume.

United States Patent [191 Gleason Nov. 13, 1973 [75] Inventor: Thomas J.Gleason, Silver Spring,

[73] Assignee: The United States of America as represented by theSecretary of the Army, Washington, DC.

[22] Filed: Sept. 27, 1971 [21] Appl. No.: 183,920

[52] US. Cl Bill/94.5, 33014.3, 313/54 [51] Int. Cl. H018 3/09, HOls3/22 [58] Field of Search 33l/94.5; 330/43; 313/54 56] References CitedUNITED STATES PATENTS 2,747,l21 5/1956 Silver 313/54 3,641,454 2/1972Krawetz 331/945 OTHER PUBLICATIONS Andriakhin et al., Journal ofExperimental and Theoretical Physics- Pis. Red. 8(7) p Oct 68, pp346-349 (corresponding English Translation Furnished pp 2 l4216) PrimaryExaminer-David Schonberg Assistant Examiner-J1. J. WebsterAttorney-Harry M. Saragovitz et all [57] ABSTRACT Method and apparatusfor triggering a discharge in a laser utilizing charged particles. Asource of charged particles injects a beam of charged particlesthroughout the discharge volume of a laser to create uniform ionizationtherein and thus trigger the electrical discharge needed to excite thelasing medium. This allows the applied electric field to be optimizedfor excitation without regard to the field required to initiate thedischarge in an un-ionized fluid. The beam of charged particlesinitiates the discharge by providing an initial ion and electronpopulation within the discharge volume. The charged particle beam may becreated by several means including a radioactive source, or artificialsources such as electron guns, par ticle accelerators, or other deviceswhich produce a directed flow of charged particles with sufficientenergy to penetrate the active lasing fluid over the entire dischargevolume.

2 Claims, 6 Drawing Figures PMENIEDIMY 13 1975 SOURCE BEAMCHARGED-PARTICLE TRIGGERED DISCHARGE FOR A LASER RIGHTS OF THEGOVERNMENT The invention described herein may be manufactured, used, andlicensed by or for the United States Government for governmentalpurposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to laser discharges, and more particularly, to a method andapparatus for triggering a discharge in a laser.

2. Description of the Prior Art The initiation of an electricaldischarge in a fluid requires a minimum electric field that is dependenton the properties of the fluid, such as for example the pressure in agas. The optimum field in the discharge after it is initiated should becontrolled by the most efficient operating point for the selectedexcitation processes which result in population inversion and lasing.This type of two step voltage optimization is often done in continuousdischarges by utilizing a high voltage pulse to initiate the dischargeand then utilizing a lower voltage to sustain the discharge at itsoptimum value for laser action. In a fast pulsed laser it is generallyimpossible to change the voltage once the pulse is started, such thatthe high voltage required to break down the gas must be utilizedthroughout the pulse, resulting in nonoptimum excitation. Overvolting toinitiate such discharges may additionally have undesirable side effects,such as corona discharges or localized discharges. Thus, it would appearthat a system for eliminating the necessity in a laser system ofapplying a breakdown voltage to trigger the discharge would be highlydesirable.

It is therefore one object of the present invention to provide a methodand apparatus for triggering a discharge in a laser that does notrequire the use of a high breakdown voltage.

Another object is to provide a method for triggering the discharge in alaser that allows the optimization of the applied electric fieldindependently of the conditions necessary to initiate the discharge.

A further object of the present invention is to provide a system fortriggering the discharge in a laser that creates a uniform ionizationthroughout the discharge volume resulting in increased efficiency andeffectiveness of the discharge in exciting the lasing medium.

SUMMARY OF THE INVENTION Briefly, in accordance with the invention, asystem is provided for triggering a discharge in a laser by injecting abeam of charged particles into the discharge volume to create uniformionization therein. The beam of charged particles initiates thedischarge by providing a high initial ion and electron population withinthe discharge volume. The use of a beam of charged particles to ionizethe fluid medium within the discharge volume allows the applied electricfield to be optimized independently of those conditions necessary toinitiate the discharge. The source of charged particles may be providedby a radioactive source such as an alpha or beta ray emitter.Alternatively, an artificial source of charged particles may beutilized, such as an electron gun, particle accelerator or other devicewhich produces a directed flow of charged particles with sufficientenergy to penetrate the active fluid throughout the discharge volume. Aunique hollow electrode structure is disclosed that may be utilized tocontain a natural radioactive source.

BRIEF DESCRIPTION OF THE DRAWINGS The specific nature of the inventionas well as other objects, aspects, uses, and advantages thereof willclearly appear from the following description and from the accompanyingdrawings, in which:

FiG. I is a schematic representation of a transverse excited lasersystem in accordance with the present invention',

FIG. 2 is a schematic representation of another embodiment of atransverse excited laser in accordance with the present invention;

FIG. 3 is a schematic illustration of an axially excited laser accordingto the teachings of the present invention;

FIG. 4 is a cross-sectional view of one embodiment of an electrode pairin accordance with the present invention',

FIG. 5 is another embodiment of an electrode pair; and

FIG. 6 illustrates another embodiment of a pair of electrodes inaccordance with the teachings of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates in schematicform one possible laser system embodying the principles of the presentinvention. Illustrated is a source of charged particles 10, a gridelectrode or thin film electrode 14, and a plate or grid electrode 16.The source of charged particles I0 may be provided by several means. Aradioactive source may be utilized to emit alpha, beta particles, orheavier decay products. Alternatively, an artificial source of chargedparticles can be used, such as for example an electron gun, a particleaccelerator or other device which produces a direct flow of chargedparticles with sufficient energy to penetrate the lasing medium over theentire region between electrodes I4 and 16. The particles may beelectrons, protons, alpha particles, or ions; in fact any convientlyproduces charged atomic or subatomic particle may be utilized inaccordance with the principles of the present invention. Such particleswould create ionization throughout their path by collisions with atomsor molecules of the active lasing medium, thus leaving a population ofions and electrons throughout the volume thus penetrated. The activelasing medium may be a gas or a liquid or a mixture of severalconstituents. Ionization may occur in any or all of the constituents andis understood not to be limited to just the lasing atom or molecule. Theuse of the beam of charged particles 12 to preionize the fluid mediumallows the applied electric field (not shown) to be optimized for laserexcitation without regard to the field required to initiate thedischarge in an un-ionized fluid. The beam of charged particles 12initiates the discharge 18 over the entire region between electrodes I4and I6, whereupon the applied electric field excites the ionized lasingmedium, thus stimulating the emission of radiation along lasing axis 15.

FIG. 2 shows another schematic illustration of a transverse excitedlaser system according to the present invention. In this system, sourceof charged particles 10 emits a beam of charged particles 12 through athin film mirror 20 that allows beam 12 to pass therethrough. Electrodes22 and 24, which may be of any well-known structure such as grids, pins,plates or wires, have an electric field applied thereto that has beenoptimized for exciting laser emission within the active medium. 11 isseen in FIG. 2 that the electrical discharge 26 is transverse to beam12, and that the lasing axis 25 is transverse to discharge path 26. Thisshows, when viewed in combination with FIG. 1 that the direction of thecharged particle beam and resultant electrical discharge can be madeindependent. Referring now to FIG. 3, a source of charged particles 10injects a beam of charged particles 12 through a thin film or ringelectrode 30 to initiate an electrical discharge 34 which excites thelasing medium in the discharge volume. Ring electrode 32 permits theaxially excited laser beam to exit along lasing axis 35.

FIGS. 4, and 6 show possible configurations of electrode pairs that maybe utilized to house a radioactive source within the context of thepresent invention. FIG. 4 shows a cross-sectional view of a pair ofelectrodes 40 and 42 that are hollowed-out in one end and contain aradioactive source of charged particles 44 and 46, respectively. Thepair of radioactive sources 44 and 46 emit a pair of charged particlebeams 48 and 50, respectively, into the discharge region of the laser.FIG. 5 illustrates a pair of electrodes 40 and 52, only the former ofwhich contains a radioactive source 44 for emitting a beam of chargedparticles 48. FIG. 6 illustrates a pair of electrodes 54 and 58, theformer of which is partially hollowed-out to contain a radioactivesource 56 that emits a beam of charged particle 60 into the dischargevolume of the laser. As is evident from the foregoing, one or both ofthe electrodes in each pair may be constructed with a hollow portion tocontain the radioactive source. The hollow portion may extend throughoutthe length of the electrode, but should be at least deep enough tocollimate the charged particle beam emerging therefrom so that itencompasses the second electrode of the set to exclusion of any thirdelectrode. This collimation can eliminate any cross-talk problems whichoccur frequently in electrode structures of this nature.

It is seen that l have provided a charged particle triggered dischargefor a laser that utilizes a beam of charged particles to create uniformionization throughout the discharge volume of a laser. The resultingcapability to optimize the discharge electric field without beinglimited to voltages high enough to create their own ionization hasheretofore been unattained. The provision of an initial population ofions and electrons uniformly distributed througout the discharge volumeis very beneficial in terms of the efficiency and effectiveness of thedischarge in exciting the lasing medium. It is apparent that theefficient volume excitation of a fluid by an electrical discharge isenhanced when the discharge is initiated stimultaneously over its entirepath, as provided by the present invention.

1 wish it to be understood that I do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

I claim as my invention:

1. A method of triggering a pulse discharge in a device for producingstimulated emission of radiation having a discharge region locatedtherein, comprising the steps of:

a. providing a laser medium within said discharge region;

b. providing electrode means about said discharge region, said electrodemeans comprising at least one pair of electrodes;

c. providing at least one collimated beam of charged particles to saiddischarge region by providing at least one radioactive pellet and atleast one electrode having a hollow open-ended portion facing thedischarge region and the other electrode of said electrode pair, saidradioactive pellet being positioned within said hollow portion foremitting said charged particle beam into said discharge region forcausing uniform ionization of said laser medium through said dischargeregion, said hollow portion being deep enough to collimate said chargedparticle beam for encompassing the other electrode of said pair oppositeto it to the exclusion of any additional electrode included in saidelectrode means;

d. applying an electric field to said discharge region via saidelectrode means for creating a population inversion is said lasermedium.

2. Apparatus for triggering a pulse discharge in a device for producingstimulated emission of radiation having a discharge region locatedtherein, comprising:

a. electrode means located about said discharge region, said electrodemeans comprising at least one pair of electrodes;

b. a laser medium located within said discharge region;

c. means for providing at least one collimated beam of charged particlesto said region comprising at least one radioactive pellet and at leastone electrode having a hollow open-ended portion facing the dischargeregion and the other electrode of said electrode pair, said radioactivepellet being posi' tioned within said hollow portion for emitting saidcharged particle beam into said discharge region for causing uniformionization of said laser medium through said discharge region, saidhollow portion being deep enough to collimate said charged particle beamfor encompassing the other electrode of said pair opposite to it to theexclusion of any additional electrode included in said electrode means;

d. means for applying an electric field to said discharge region viasaid electrode means for creating a population inversion in said lasermedium.

1. A method of triggering a pulse discharge in a device for producingstimulated emission of radiation having a discharge region locatedtherein, comprising the steps of: a. providing a laser medium withinsaid discharge region; b. providing electrode means about said dischargeregion, said electrode means comprising at least one pair of electrodes;c. providing at least one collimated beam of charged particles to saiddischarge region by providing at least one radioactive pellet and atleast one electrode having a hollow Open-ended portion facing thedischarge region and the other electrode of said electrode pair, saidradioactive pellet being positioned within said hollow portion foremitting said charged particle beam into said discharge region forcausing uniform ionization of said laser medium through said dischargeregion, said hollow portion being deep enough to collimate said chargedparticle beam for encompassing the other electrode of said pair oppositeto it to the exclusion of any additional electrode included in saidelectrode means; d. applying an electric field to said discharge regionvia said electrode means for creating a population inversion is saidlaser medium.
 2. Apparatus for triggering a pulse discharge in a devicefor producing stimulated emission of radiation having a discharge regionlocated therein, comprising: a. electrode means located about saiddischarge region, said electrode means comprising at least one pair ofelectrodes; b. a laser medium located within said discharge region; c.means for providing at least one collimated beam of charged particles tosaid region comprising at least one radioactive pellet and at least oneelectrode having a hollow open-ended portion facing the discharge regionand the other electrode of said electrode pair, said radioactive pelletbeing positioned within said hollow portion for emitting said chargedparticle beam into said discharge region for causing uniform ionizationof said laser medium through said discharge region, said hollow portionbeing deep enough to collimate said charged particle beam forencompassing the other electrode of said pair opposite to it to theexclusion of any additional electrode included in said electrode means;d. means for applying an electric field to said discharge region viasaid electrode means for creating a population inversion in said lasermedium.